The oxygen heterocyclic fraction of bergamot oil has undoubtedly received more attention than that of any other citrus oil. Bergamot oil is a very valuable product, largely used in perfumery as the basis of eau de cologne, and in cosmetics as a constituent of suntan products. It is known to have strong photosensitizing activity, due to the presence of psoralens and, in particular, bergapten. This has prompted the development of analytical procedures for the determination of bergapten in bergamot oil and in cosmetic products containing the oil. The early studies on the composition of the oxygen heterocyclic fraction of bergamot oil have been reviewed by Mossman and Bogert (1941) and, more recently, by Di Giacomo and Calvarano (1978a, 1978b), Lawrence (1982, 1994), Dugo and McHale (2002), and Dugo and Russo (2011).